1. Field of the Invention
The present invention relates generally to polycrystalline diamond compact (PDC) drill bits, and specifically to directional drilling with PDC drill bits.
2. Description of the Prior Art:
In exploring earth formations for oil and gas reserves, it is sometimes useful to drill a hole which is deviated from a vertical position to a substantially horizontal position. However, it is sometimes desirable to drill backward toward a vertical position from a horizontal wellbore.
In certain earth formations, it is desirable to use a polycrystalline diamond compact (PDC) drill bit. Unfortunately, most PDC drill bits do not walk to the right, so it is difficult to correct or change the deviation of a wellbore.
The directional tendencies of oil well drilling bits can be critical to the efficient penetration of oil and gas payzones. The increase in high angle and horizontal well path designs has made bit lateral deviation characteristics, known as bit walk or bit turn, of greater concern.
Rolling cone drill bits have always demonstrated a tendency to turn, or walk, to the right. This is due to the fact that they experience very minimal left hand reactive torque and to the fact that they can experience a drop, bite and fling progression which will be described in more detail below.
PDC bits have nearly always demonstrated a tendency to turn to the left. This is due to their fixed cutting structure creating a hard left hand reactive torque while drilling In prior art, a few PDC bit models have been observed to run in a neutral turn mode and one model has been noted to have a right turn tendency. Heretofore bit designers and directional drillers have not understood the mechanics of PDC bit turn but have only classified and predicted turn tendencies based on field experience.